Dual-Layer Three-Way Catalyst for Exhaust Purification
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Solution Overview
Problem
Current exhaust gas purification systems using three-way catalysts face challenges in improving the removal rates of hydrocarbon, carbon monoxide, and nitrogen oxide, particularly in maintaining effective purification at varying temperatures and air-fuel ratios.
Innovation Solution
The system incorporates a dual-layer three-way catalyst structure with an upstream catalyst layer containing Pd, Rh, and ceria, and a downstream catalyst layer with a higher ceria content, optimized to enhance hydrocarbon removal while maintaining carbon monoxide and nitrogen oxide removal efficiency, by controlling the distribution and density of noble metals and ceria within the catalyst layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ceria content is increased to improve hydrocarbon removal rate, then the hydrocarbon removal rate is improved, but the thermal degradation resistance deteriorates
Solution Approach 1:
The patent applies local quality by creating two distinct catalyst layers with different ceria content distributions. The downstream catalyst layer has high ceria content (5-20 mass%) to maximize hydrocarbon removal, while the upstream catalyst layer has low ceria content (0-5 mass%) to resist thermal degradation. This spatial differentiation of material properties resolves the contradiction between removal efficiency and thermal stability.
Solution Approach 2:
The three-way catalyst is segmented into two functional layers: an upstream catalyst layer and a downstream catalyst layer. Each layer performs a specialized function - the upstream layer focuses on thermal stability and CO/NOx removal, while the downstream layer focuses on hydrocarbon removal. This segmentation allows the system to achieve both high hydrocarbon removal and thermal degradation resistance simultaneously.
2Productivity
If the noble metal content is increased to improve removal efficiency, then the removal efficiency is improved, but the manufacturing cost increases
Solution Approach 1:
The patent optimizes noble metal distribution by concentrating Pd and Rh in the downstream catalyst layer where they are most needed for hydrocarbon removal. The upstream catalyst layer uses minimal noble metals, relying instead on the OSC material for its purification function. This localized allocation of expensive noble metals improves removal efficiency while controlling manufacturing costs.
Solution Approach 2:
The patent changes the concentration parameters of noble metals and OSC materials between the two catalyst layers. By adjusting these compositional parameters - high Pd/Rh in downstream, low in upstream; high OSC in downstream, low in upstream - the system achieves optimal removal efficiency at reduced overall noble metal content, thereby lowering manufacturing cost.
3Temperature
If the catalyst layer is designed for high temperature performance, then the high temperature removal efficiency is improved, but the low temperature performance deteriorates
Solution Approach 1:
The patent segments the catalyst function across temperature ranges by creating two layers with different compositional characteristics. The upstream catalyst layer with low ceria and minimal noble metals is optimized for low-temperature CO and NOx removal. The downstream catalyst layer with high ceria and Pd/Rh is optimized for high-temperature hydrocarbon removal. This segmentation enables the system to maintain high performance across both temperature extremes.
Solution Approach 2:
The patent uses composite material design by combining different catalyst components (noble metals, OSC materials, support materials) in specific ratios and distributions within each layer. The upstream layer uses a composite optimized for low-temperature reactions, while the downstream layer uses a composite optimized for high-temperature hydrocarbon oxidation. This composite approach allows simultaneous optimization for both temperature conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves the removal rate of hydrocarbons and nitrogen oxides, while preventing thermal degradation and maintaining engine power, even at lower exhaust gas temperatures and fluctuating air-fuel ratios, thus enhancing overall exhaust gas purification performance.
Implementation Method 1
an OSC material containing at least ceria
Implementation Method 2
The three-way catalyst oxidizes hydrocarbon into water and carbon dioxide (CO2)
Implementation Method 3
oxidizes carbon monoxide into carbon dioxide
Implementation Method 4
reduces nitrogen oxide into nitrogen (N2)
Data Source
AI summary
An exhaust gas purification apparatus includes a three-way catalyst. The three-way catalyst includes a downstream catalyst layer and an upstream catalyst layer. The downstream catalyst layer is to be provided in an exhaust pipe. The downstream catalyst layer contains a noble metal material containing at least one of Pd, Rh, or Pt, and an OSC material containing at least ceria. The upstream catalyst layer is to be provided in the exhaust pipe closer to an engine than the downstream catalyst layer is. The upstream catalyst layer contains the noble metal material and the OSC material. The upstream catalyst layer contains the ceria at a content less than a content of the ceria in the downstream catalyst layer.